1. Technical Field of the Invention
The present invention relates generally to a seat occupant sensor equipped with a stopper mechanism which has a cantilevered elastic sensing plate working to determine the presence or absence and/or the size of a person on a seat, and more particularly to a stopper mechanism for such a sensor which works to permit the degree of bending of the sensing plate to be maximized without causing mechanical damage thereto.
2. Background Art
Japanese Patent First Publication Nos. 2002-243528 and 9-207638 teach a seat occupant discrimination system for automotive vehicles equipped with an airbag for protecting a passenger from an accidental collision. The seat occupant discrimination system includes a plurality of seat occupant sensors. The seat occupant sensors are implemented by load sensors which are installed beneath a seat of the vehicle at different locations. Each of the seat occupant sensors is responsive to part of a weight load of a passenger on the seat to output a signal indicative thereof. The seat occupant discrimination system finds the sum of outputs from all the seat occupant sensors to determine whether the seat is occupied or not and/or whether an occupant on the seat is an adult or a child.
Some of seat occupant sensors of the type as described above have an elastic sensing plate cantilevered by a stationary support member fixed on a floor pan of the vehicle. The sensing plate has a plurality of strain gauges affixed to the surface thereof. Application of a physical load from the seat to the sensing plate causes the sensing plate to be bent. The strain gauges output a signal as a function of the degree of bending of the sensing plate. The signal is used to determine whether the seat is occupied or not and/or whether an occupant on the seat is an adult or a child for controlling actuation of an automotive airbag. For example, Japanese Patent First Publication No. 2000-258234 (U.S. Pat. No. 6,571,647 B1) discloses such a type of sensing plate.
When an excessive load is applied to the sensing plate, it may result in plastic deformation or fracture thereof. In order to avoid this problem, a protective stopper may be installed on the stationary support member. When the load is applied to around the center of the bottom of the seat, it will cause the sensing plate to be bent in the form of an ideal extended S-curve. In this case, the stopper may be located anywhere on the stationary support member. Alternatively, when a passenger sits reclining his or her back on the seat strongly, so that a great load is applied to the back of the seat, it will cause the rotation moment to be applied to the seat. The rotation moment may cause the sensing plate to be bent in the form deviating from the S-curve. In this case, it may be impossible for the stopper to avoid the degree of bending of the sensing plate exceeding the bending stress limit thereof depending upon the location of the stopper.